The Arduino Opta and commercial ESP32 PLCs solve a similar problem:
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take an embedded microcontroller + add industrial voltage I/O + add DIN-rail mounting + add fieldbus/network interfaces + make it practical inside a control cabinet |
But the two approaches are quite different.
Arduino Opta is a compact, highly standardised micro PLC based on:
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STM32H747XI → Cortex-M7 up to 480 MHz → Cortex-M4 up to 240 MHz 8 × digital / 0-10 V analogue inputs 4 × 10 A relay outputs Ethernet optional RS-485 optional Wi-Fi/BLE IEC 61131-3 PLC IDE secure element |
The current commercial ESP32 PLC family from Industrial Shields uses:
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→ dual-core Xtensa LX6 → up to 240 MHz → 520 KB SRAM → 16 MB Flash industrial 5-24 V I/O 0-10 V analogue I/O PWM outputs Ethernet Wi-Fi Bluetooth RS-485 RS-232 Arduino IDE |
The most important difference is:
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Opta → compact standardised PLC → configurable industrial controller family with much wider I/O counts |
Quick Comparison
| Feature | Arduino Opta | Commercial ESP32 PLC |
|---|---|---|
| Main processor | STM32H747XI | ESP32-WROOM-32UE |
| CPU architecture | Cortex-M7 + Cortex-M4 | Dual-core Xtensa LX6 |
| Maximum CPU clock | M7 480 MHz + M4 240 MHz | Up to 240 MHz |
| RAM | 1 MB STM32 RAM | 520 KB SRAM |
| Flash | 2 MB internal + 16 MB QSPI | 16 MB module Flash |
| Base inputs | 8 digital / 0-10 V analogue | Model dependent; much larger ranges available |
| Base outputs | 4 × normally-open relays | Digital, PWM, 0-10 V and/or relay depending on model |
| Relay rating | Up to 10 A per relay under specified conditions | Model dependent; current relay models typically lower per-contact ratings |
| Ethernet | 10/100 RJ45 | Ethernet via W5500-based interface |
| Wi-Fi/BLE | Opta WiFi only | Native ESP32 Wi-Fi/BLE across current family |
| RS-485 | RS485 and WiFi variants | Native half-duplex RS-485 |
| RS-232 | No native RS-232 terminal | Available natively |
| PLC languages | Arduino PLC IDE / IEC 61131-3 | Primarily Arduino IDE C/C++ |
| Expansion | Up to five Opta expansion modules | Large I/O family + extensive I2C/module expansion |
| Security chip | ATECC608B secure element | ESP32 hardware security, board-family dependent |
| Best fit | Compact PLC, building automation, IEC programming | High-I/O custom automation and Arduino-centric control |
Processor: STM32H747 vs ESP32
Opta uses the:
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STM32H747XI |
with two different Arm cores:
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Cortex-M7 → up to 480 MHz Cortex-M4 → up to 240 MHz |
This is a substantially more powerful MCU architecture than the classic ESP32 used in current Industrial Shields ESP32 PLCs.
ESP32 PLC CPU
The current family uses:
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1 2 3 4 |
ESP32-WROOM-32UE |
with:
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2 × Xtensa LX6 80-240 MHz 520 KB SRAM 16 MB Flash FreeRTOS |
This is still more than sufficient for:
- machine sequencing;
- Modbus;
- MQTT;
- web interfaces;
- Wi-Fi communication;
- digital control;
- analogue acquisition.
Opta Has More CPU Headroom
The STM32H747 is a better fit for applications involving:
- large control algorithms;
- high-rate data acquisition;
- predictive-maintenance calculations;
- dual-core task separation;
- large communication stacks;
- more demanding real-time workloads.
ESP32 PLC Has the Wireless Stack in the Main MCU
With an ESP32 PLC:
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control logic + Wi-Fi + Bluetooth + FreeRTOS |
all run on the ESP32 itself.
This keeps the architecture simple and familiar for ESP32 developers.
Input Count Is Where ESP32 PLCs Become Interesting
Opta has:
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8 inputs |
in its base unit.
The current Industrial Shields ESP32 PLC family spans many configurations, including models with roughly:
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19 21 38 42 50+ I/O points |
depending on the selected model and output mix.
Example: ESP32 PLC 21
A representative 21-I/O model provides approximately:
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6 × analogue/digital inputs 7 × isolated digital inputs 5 × isolated digital outputs 3 × digital/PWM/analogue outputs |
That is already a much larger base I/O set than Opta.
Example: ESP32 PLC 38R
A relay-heavy model provides approximately:
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8 × analogue/digital inputs 4 × isolated digital inputs 6 × digital/PWM/analogue outputs 16 × relay outputs |
This illustrates the biggest ESP32 PLC advantage:
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you can choose an I/O mix closer to the machine |
Opta Is Much More Standardised
Every Opta base unit gives you:
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8 inputs 4 relays Ethernet USB-C |
with RS-485 and wireless depending on variant.
This makes BOM selection simpler because there are only three communication variants.
Opta Inputs Are Dual-Purpose
The eight Opta inputs:
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1 2 3 4 |
I1-I8 |
can operate as:
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0-24 V digital inputs or 0-10 V analogue inputs |
ESP32 PLC Analogue Inputs
Representative ESP32 PLC models provide:
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1 2 3 4 |
0-10 V analogue inputs |
that can also be used as digital inputs.
Current Industrial Shields documentation also describes configurable 4-20 mA capability on parts of the modern family.
Opta Base Unit Has No Analogue Output
This is an important limitation of the base Opta.
The four outputs are:
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1 2 3 4 |
mechanical relays |
not:
- 0-10 V outputs;
- 4-20 mA outputs;
- PWM transistor outputs.
Analogue output requires an Opta expansion module or external hardware.
ESP32 PLCs Can Include 0-10 V / PWM Outputs
Many ESP32 PLC models include outputs configurable as:
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digital PWM 0-10 V analogue |
depending on model.
This can simplify applications such as:
- VFD speed references;
- damper control;
- valve positioning;
- lighting control;
- analogue actuator commands.
Relay Outputs
Opta provides:
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1 2 3 4 |
4 × SPST-NO relays |
rated up to:
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1 2 3 4 |
10 A |
per relay under the specified load conditions.
ESP32 PLC Relay Options
Relay-equipped ESP32 PLC models range from:
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8 relays to 16 relays and beyond |
depending on model.
The trade-off is that contact ratings and load categories must be checked for the selected unit rather than assumed from Opta’s specification.
For Large Relay Counts, ESP32 PLC Can Be Cleaner
If the machine requires:
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12 16 24 relay channels |
choosing a PLC with those outputs already integrated can be cleaner than stacking multiple expansion modules.
Ethernet
All current Opta variants include:
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10/100 Ethernet RJ45 |
which makes wired industrial networking standard across the range.
ESP32 PLC Ethernet
Current Industrial Shields ESP32 PLCs also include wired Ethernet using a:
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1 2 3 4 |
Ethernet controller connected to the ESP32 over SPI.
This gives a hardware TCP/IP Ethernet interface suitable for:
- Modbus TCP;
- MQTT;
- HTTP;
- SCADA;
- LAN monitoring.
Wi-Fi and Bluetooth
Opta only includes wireless on:
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1 2 3 4 |
Opta WiFi |
The Lite and RS485 versions are wired-only.
ESP32 PLC Has Native Wireless
Current ESP32 PLC models expose the ESP32’s:
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1 2 3 4 5 |
2.4 GHz Wi-Fi Bluetooth / BLE |
as part of the standard platform.
This can be useful for:
- wireless commissioning;
- MQTT;
- cloud telemetry;
- local web interfaces;
- BLE devices.
RS-485
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1 2 3 4 |
no RS-485 |
Opta RS485 and Opta WiFi:
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1 2 3 4 |
half-duplex RS-485 |
ESP32 PLC RS-485
The current ESP32 PLC family includes:
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1 2 3 4 |
half-duplex RS-485 |
using an onboard MAX485-class transceiver.
It supports industrial protocols such as:
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1 2 3 4 |
Modbus RTU |
RS-232 Is an ESP32 PLC Advantage
Opta has no native RS-232 terminal.
Commercial ESP32 PLCs in this family include:
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1 2 3 4 |
RS-232 |
alongside RS-485.
This is useful when integrating:
- legacy instruments;
- barcode readers;
- old serial HMIs;
- industrial scales;
- serial printers.
Modbus TCP
Both platforms can implement:
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Modbus TCP |
over Ethernet.
Modbus RTU
Opta requires the:
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RS485 or WiFi |
variant for native Modbus RTU hardware.
ESP32 PLC models already provide RS-485 as part of the communications stack.
Programming Philosophy Is Very Different
Opta is intentionally positioned as both:
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Arduino controller and IEC 61131-3 PLC |
Arduino PLC IDE
Opta supports:
- Ladder Diagram;
- Structured Text;
- Function Block Diagram;
- Sequential Function Chart;
- Instruction List in Arduino PLC IDE.
This is important for automation engineers who expect PLC programming rather than only embedded C++.
ESP32 PLC Is Primarily Arduino IDE C/C++
The current Industrial Shields ESP32 PLC documentation focuses on:
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Arduino IDE C/C++ FreeRTOS Industrial Shields board package |
This is very attractive for developers already comfortable with:
- ESP32;
- Arduino libraries;
- C++ classes;
- FreeRTOS tasks;
- Wi-Fi programming.
Opta Has the Stronger Traditional PLC Workflow
If the engineering team expects:
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Ladder Structured Text Function Blocks |
Opta has a much more direct fit.
ESP32 PLC Has the Stronger Arduino/ESP32 Workflow
If the team thinks in:
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setup() loop() FreeRTOS MQTT WiFi Arduino libraries |
the ESP32 PLC can feel more natural.
Security
Opta includes a dedicated:
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ATECC608B |
secure element for:
- device identity;
- private-key protection;
- X.509 authentication;
- secure provisioning;
- cloud credentials.
ESP32 Security
The ESP32 provides hardware security features including:
- secure boot;
- Flash encryption;
- hardware cryptography;
- eFuses.
But a separate secure-element implementation depends on the exact commercial PLC design.
Opta Has a More Explicit Security Story
Arduino positions Opta around:
- hardware-backed identity;
- secure OTA;
- Arduino Cloud;
- X.509 support;
- production cybersecurity maintenance.
This can simplify secure connected-product design.
Expansion
Opta supports:
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up to 5 snap-on expansion modules |
through its side connector.
These can add:
- digital inputs;
- relay outputs;
- solid-state outputs;
- analogue inputs;
- analogue outputs.
ESP32 PLC Expansion
Industrial Shields offers:
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large base I/O models + I2C expansion + additional communication boards |
Current product pages describe support for very large external expansion counts on selected models.
Different Expansion Philosophy
Opta starts small:
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8 inputs 4 relays |
and grows through side-mounted modules.
ESP32 PLC lets you choose a much larger base PLC before adding expansion.
DIN-Rail Installation
Both product families are designed for:
- DIN-rail mounting;
- 24 V cabinet supplies;
- screw terminal wiring;
- industrial sensors and actuators.
Neither should be confused with a bare ESP32 development board mounted inside a plastic box.
Certifications
Arduino’s current Opta documentation lists certifications including:
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CE UKCA FCC cULus ENEC CB |
Industrial Shields also publishes CE/UKCA and model-specific certification documentation for current ESP32 PLC products.
For a production machine, verify the exact model and jurisdiction rather than assuming every ESP32-based PLC has identical approvals.
Which Is Better for a Small Building-Automation Panel?
Opta is particularly neat when the requirement is:
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8 inputs 4 relay outputs Ethernet Modbus PLC logic |
because it is extremely compact.
Which Is Better for 30+ I/O?
An ESP32 PLC model with the required I/O already onboard can reduce:
- module count;
- inter-module wiring;
- panel width;
- configuration complexity.
Which Is Better for Lots of 0-10 V Outputs?
ESP32 PLC can be attractive because several models expose analogue/PWM outputs in the base unit.
Opta needs an analogue expansion for equivalent process outputs.
Which Is Better for Four High-Current Relay Loads?
Opta’s:
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4 × 10 A normally-open relays |
are convenient when exactly a few relatively high-current switched loads are required.
Which Is Better for Many Relay Outputs?
A relay-heavy ESP32 PLC variant can integrate:
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1 2 3 4 5 6 |
8 16 24 |
relays depending on the selected model.
Which Is Better for IEC 61131-3?
Opta.
Arduino PLC IDE is a first-class part of the product platform.
Which Is Better for ESP32 Developers?
ESP32 PLC.
The familiar:
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Arduino-ESP32 FreeRTOS Wi-Fi Bluetooth |
stack reduces the learning curve for developers already using ESP32.
Which Is Better for Predictive Maintenance?
Opta has more compute headroom with its:
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480 MHz Cortex-M7 + 240 MHz Cortex-M4 |
architecture.
For local signal processing, advanced analytics and simultaneous communications, this can matter.
Which Is Better for Wi-Fi?
If Wi-Fi is mandatory:
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Opta → choose Opta WiFi ESP32 PLC → Wi-Fi is inherent to the ESP32 platform |
Which Is Better for RS-232?
ESP32 PLC, because the current Industrial Shields family provides a native RS-232 interface.
Which Is Better for Simplicity?
Opta has the simpler product matrix:
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Lite RS485 WiFi |
with identical base I/O.
ESP32 PLC offers many more I/O combinations, which is more flexible but requires more careful model selection.
Decision Table
| Requirement | Better fit |
|---|---|
| IEC 61131-3 / Ladder / ST | Arduino Opta |
| Highest CPU headroom | Arduino Opta |
| Dedicated secure element | Arduino Opta |
| Compact 8-input / 4-relay PLC | Arduino Opta |
| Four 10 A relay outputs | Arduino Opta |
| Arduino Cloud / secure OTA integration | Arduino Opta |
| Large base I/O count | ESP32 PLC |
| Many relay outputs | ESP32 PLC |
| 0-10 V outputs in base PLC | ESP32 PLC |
| PWM transistor outputs | ESP32 PLC |
| Native RS-232 | ESP32 PLC |
| ESP32/FreeRTOS familiarity | ESP32 PLC |
| Native Wi-Fi across product family | ESP32 PLC |
| Ethernet | Both |
| RS-485 / Modbus RTU | Both with correct Opta variant |
Quick Reference
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Arduino Opta STM32H747XI M7 @ 480 MHz M4 @ 240 MHz 1 MB RAM 2 MB internal Flash 16 MB QSPI 8 × 0-24 V digital / 0-10 V analogue inputs 4 × NO relays 10 A max per relay under specified conditions 10/100 Ethernet RS-485 on RS485/WiFi models Wi-Fi/BLE on WiFi model ATECC608B Arduino IDE Arduino PLC IDE IEC 61131-3 up to 5 expansion modules Representative commercial ESP32 PLC family ESP32-WROOM-32UE 2 × Xtensa LX6 @ up to 240 MHz 520 KB SRAM 16 MB Flash 5-24 V industrial inputs 0-10 V analogue inputs digital/PWM/analogue outputs relay variants Ethernet Wi-Fi Bluetooth/BLE RS-485 RS-232 Arduino IDE FreeRTOS large base-I/O model range |
Final Thoughts
Arduino Opta and ESP32 PLCs are not simply interchangeable PLCs with different processors.
Opta is designed around:
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compact standardised hardware + strong STM32H747 processing + IEC 61131-3 + secure industrial IoT + snap-on expansion |
A commercial ESP32 PLC is designed around:
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large configurable I/O sets + native Wi-Fi/BLE + Arduino/FreeRTOS programming + 0-10 V / PWM outputs + RS-232 / RS-485 |
If the project needs a conventional PLC workflow, four substantial relay outputs, secure cloud integration and a compact standard unit, Opta is a particularly coherent platform.
If the project needs 20, 40 or 50+ I/O points, multiple analogue/PWM outputs, many relays or an ESP32-native programming environment, a commercial ESP32 PLC can reduce the amount of expansion hardware required.
For the complete Opta terminal mapping, see our Arduino Opta pinout and I/O guide. For choosing between Arduino’s three versions, see Arduino Opta Lite vs RS485 vs WiFi.